1. Field of the Invention
The present invention relates to a bearing arrangement and more specifically to a locking mechanism for securing a shaft in a bearing.
2. Description of the Prior Art
Conventional techniques for locking flanged, pillow-block, cartridge, and the like type of bearings to a shaft include, but are not limited to dual setscrew attachments (typically 2 screws at 65 degrees); tapered sleeves; and centering collars.
In the case of roller element type bearings such as spherical bearings, special care must be taken to ensure the internal clearances of the bearing are not compromised (diminished to such a degree the bearing will not process effectively at load and speed). Presently, the two most common methods of securing this type of bearing to a shaft are the dual setscrews and tapered sleeves.
The dual setscrew type clamping arrangement is the simplest method of securing a spherical bearing to a shaft. An example of this type of arrangement is shown in FIGS. 1A, 1B and 2. This arrangement has two setscrews 10 threaded into a locking collar 11. The setscrews 10 extend through clearance holes 12 formed in the bearing internal sleeve 14, and bear on the shaft surface.
This mechanism does not impact the internal clearance of the bearing 14, but suffers from a number of drawbacks. Flats must be provided on the shafts and the two screws 10 must always be carefully torqued to specified levels to ensure that the appropriate gripping action is developed. Further, the screws must be replaced with new ones each time the collar is released because the tip of each setscrew is deformed by its initial use and will not produce the desired engagement if reused. In the event that the correct types of setscrews are not used, i.e., cup tipped setscrews, during the replacement, then the necessary relative rotation preventing grip will not be produced. If these requirements are not met, the locking action of the collar may be lost. This loss, of course, leads to slippage and undesirable detrimental effects.
Another drawback of this type of locking mechanism is the shaft becomes eccentric to the bearing by virtue of pulling the clearance between the sleeve and the shaft in one direction. Furthermore, the integrity of the connection depends on the setscrews maintaining their preload under various process conditions including vibrations, cyclic loading, etc.
Another technique of securing a spherical bearing is through a pair of tapered sleeves. With this arrangement, the inside diameter of the inner sleeve, typically split axially, is secured to the OD (outer diameter) of the shaft, while the OD of the outer sleeve is simultaneously secured to the ID (inner diameter) of the bearing race. By forcing the inner and outer sleeves toward one another along the shaft, the inner race of the bearing is expanded. This induces the drawback that the internal clearance between the rollers and the race elements tend to be diminished. Inasmuch as these type bearings have specific dimensional tolerances it is imperative to ensure that the degree of tightening is carefully controlled so that it provides the required connection but does not induce distortion that inhibits proper functioning of the bearing.
FIG. 3 shows a variant of this tapered sleeve technique. This arrangement differs in that the inner race 22 of the bearing 20 is tapered and is arranged to cooperate with the split tapered sleeve which is inserted thereinto.
The centering collar arrangement (not illustrated), while being less common than the above mentioned dual setscrew and tapered sleeve arrangements, is a known arrangement for attachment of radial bearings. This arrangement centers the bearing onto the shaft, and provides a positive method of clamping. Unfortunately, this arrangement is not recommended for spherical bearings due to possible distortion of the inner race and its effects on the internal clearances, and for lack of grip due to cantilevered flexed fingers and their inherent lack of surface area contact with the shaft.